The present invention relates to heat management systems, and more particularly to a high efficiency heat transfer system for transporting heat from a plurality of heat sources to one or more heat sinks. The invention, while described in some particulars with reference to spacecraft and space platform thermal management, will be seen to have perhaps even greater utility in terrestrial applications.
Heretofore, heat management and transfer systems have been predominantly passive circulation single phase (convective type), forced circulation single phase, forced circulation two phase, or passive circulation two phase. The forced circulation technologies typically involve considerable temperature gradients (and if phase change is involved there are also usually considerable pressure gradients). The "passive" circulation systems include, among others, the "absorption cycle" type and the heat pipe. Both of these two phase passive circulation technologies involve only small pressure gradients, and the heat pipe usually maintains a fairly constant temperature throughout. The advantages and disadvantages of the various technologies are well known, of course, to practitioners in the art.
For the past 20 years (starting with Gemini), the thermal management of manned spacecraft has relied on pumped (forced circulation) single phase liquid systems to collect, transport, and reject waste heat via a radiator. These systems have performed with excellent reliability. Evolving future space stations and platforms, however, will require a much more significant thermal management role because of multi-year mission durations, larger space station and platform sizes, the resulting longer physical distances involved in transporting the heat, larger quantities of waste heat to be dissipated, and the variety of payloads and missions which must be accommodated. Single phase pumped liquid systems become less and less attractive in such cases, due to such factors as weight, the energy needed to circulate sufficient liquid to accommodate the heat transfer loads, sometimes objectionable temperature differentials, limitations on system flexibility, and limited growth capability.
A review of such prior art patents as the following shows that they fail to teach or suggest a suitable solution to the above needs. For example, U.S. Pat. No. 2,448,261 (Gaugler, issued Aug. 31, 1948) discloses a type of heat pipe. However, as is well known, heat pipes of this type depend upon capillary action as the sole liquid transport mechanism. This places a limitation upon the overall capacity of the system to transport fluid, and thus to transport heat. Also, there is no active means for adjusting flow rates in response to local conditions.
U.S. Pat. No. 4,131,158 (Abhat et al., issued Dec. 26, 1978) shows a heating and heat storing system using a heat pipe therein. Again, the heat pipe is a passive circulation device, utilizing capillary action to circulate the operating liquid.
U.S. Pat. No. 4,177,858 (Daman et al., issued Dec. 11, 1979) discloses a heat exchanger using heat pipes to transfer heat between two separate fluid carrying chambers. Once again, the heat pipes are of the passive circulation/capillary action type.
U.S. Pat. No. 4,312,402 (Basiulis, issued Jan. 26, 1982) discloses an osmotically pumped heat transfer system employing a closed heat pipe together with solvent and solute-solvent mixture reservoirs separated from each other by a solvent permeable membrane.
U.S. Pat. No. 4,352,392 (Eastman, issued Oct. 5, 1982) shows a mechanically assisted method for supplying liquid to an evaporator surface, using a pump and a nozzle spray mechanism to improve distribution of the liquid over the evaporator surface. The pump is merely for providing the spray, and supplies a constant amount of liquid regardless of the needs or demands of the evaporator surface. It does not operate to improve circulation from a condenser to an evaporator and back. It does not pull/push vapor and liquid through a heat transfer circuit. Also, due to the need to disintegrate the fluid stream into a spray of small droplets, the pump pressure/energy parameters can be expected to be greater than with a lower pressure system which simply circulates the coolant.
U.S. Pat. No. 4,437,510 (Martorana, issued Mar. 20, 1984) discloses a heat pipe having an internal check valve located in the vapor channel of the heat pipe. The check valve, which is operated by very low pressure, allows vapor to flow only in a forward direction from a heat source to a heat sink. When the heat sink becomes hotter than the heat source, the valve blocks vapor flow in the reverse direction.
U.S. Pat. No. 4,467,861 (Kiseev at al., issued Aug. 28, 1984) shows a vapor jet pump heat transfer device described as using vapor pressure generated by the evaporation of a liquid working fluid to propel heated liquid working fluid through a heat exchanger where heat is lost to a heat sink. The liquid then returns back to a chamber from which capillary forces move the liquid working fluid into the evaporation area where heat from the heat source evaporates the liquid working fluid again. The vapor thus generated is described as operating a vapor jet pump, completing the cycle. The heat transfer is thus by heating and cooling of a liquid rather than by transfer to a heat sink by the working fluid vapor phase.
U.S. Pat. No. 4,467,862 (DeBeni, issued Aug. 28, 1984) discloses a passive heat transport system. An evaporator containing a liquid working fluid and in thermal communication with a heat source is connected by a tube to a condenser, itself in thermal communication with a heat sink. In a preferred embodiment the condenser contains a non-condensible gas. Heat from the source vaporizes the working fluid which, through gaseous expansion, is propelled to the condenser where it condenses to a liquid and compresses the non-condensible gas. Upon removal of the heat source (cooling the boiler), the compressed non-condensible gas expands, forcing the liquid working fluid back through the tube to the evaporator, completing the cycle. As understood, the device will also work when the boiler dries out even while still hot.
A need therefore remains for a light weight heat transfer system requiring minimal energy to circulate the necessary fluid to accommodate the system heat transfer loads; which need not operate with sometimes objectionable temperature differentials across the system; which offers maximum system flexibility and growth capability, high reliability, and low complexity. Such a system should also be inexpensive, durable, versatile, uncomplicated, reliable, inexpensive to manufacture, and readily suited to the widest possible utilization in terrestrial as well as space applications.